The storage of hydrogen in the form of metal hydrides has gained a lot of attention in the recent years. Storage of hydrogen in metal hydrides has the advantage over storage of for instance liquid or compressed hydrogen in that it does not require the use of low temperatures or excessive pressures. A disadvantage of the use of metal hydrides is relatively low storage density per weight of storage material (expressed in wt % of H2 per weight of metal hydride) and slow reversible absorption and desorption kinetics. A prime candidate for storing hydrogen in metal hydrides is NaAlH4. With NaAlH4 a storage density per weight of storage material of up to 5 wt % of hydrogen can be attained. In for instance U.S. Pat. No. 6,106,801 it has been disclosed that the process of hydrogen release and uptake by alkali metal alanates can be accelerated or made to proceed more complete by the addition of catalyst, in particular with a compound of a transition metal of group 3 or 4 of the Periodic Table of Elements. As preferred dopants are mentioned: alcoholates, halides, hydrides and organo-metallic and inter-metallic compounds of the mentioned metals. U.S. Pat. No. 6,106,801 specifically mentions doping of NaAlH4 with TiCl3, TiCl4 and Ti(OBu)4. However, in practice, the rate of hydrogen uptake is of these materials is still too small for commercial application in for instance automotive applications.